An magnetoresistance random access memory (MRAM) includes an array of memory cells. Each memory cell is a magnetic tunnel junction device. The magnetic tunnel junction device operates on the principles of spin tunneling. There are several types of magnetic tunnel junction devices including two prominent types, tunneling magnetoresistance (TMR) and giant magnetoresistance (GMR). Both types of devices comprise several layers of thin film materials and include a first layer of magnetic material in which a magnetization is alterable and a second layer of magnetic material in which a magnetization is fixed or “pinned” in a predetermined direction. The first layer is commonly referred to as a data layer or a sense layer; whereas, the second layer is commonly referred to as a reference layer or a pinned layer. The data layer and the reference layer are separated by a very thin tunnel barrier layer. In a TMR device, the tunnel barrier layer is a thin film of a dielectric material (e.g. silicon oxide SiO2). In contrast, in a GMR device, the tunnel barrier layer is a thin film of an electrically conductive material (e.g. copper Cu).
Electrically conductive traces, commonly referred to as word lines and bit lines, or collectively as write lines, are routed across the array of memory cells with a memory cell positioned at an intersection of a word line and a bit line. The word lines can extend along rows of the array and the bit lines can extend along columns of the array, or vice-versa. A single word line and a single bit line are selected and operate in combination to switch the alterable orientation of magnetization in the memory cell located at the intersection of the word line and the bit line. A current flows through the selected word and bit lines and generates magnetic fields that collectively acts on the alterable orientation of magnetization to cause it to switch (i.e. flip) from a current state (i.e. a logic zero “0”) to a new state (i.e. a logic “1”).
One problem in prior magnetic tunnel junction devices is that the electrically conductive materials that are used for the write lines can become shorted to each other and/or can cause a short between the data and reference layers. As a result, the short causes a resistance of the prior magnetic tunnel junction device to be too low and therefore the state of the alterable orientation of magnetization cannot be sensed by measuring a resistance across the magnetic tunnel junction device or by sensing a magnitude of current flow through the magnetic tunnel junction device. Consequently, the short is a defect that renders the magnetic tunnel junction device inoperable.
In FIG. 1, a prior magnetic tunnel junction device 200 includes a magnetic tunnel junction stack 230 that is crossed by and positioned between a column conductor 201 and a row conductor 213. A current lx flowing in the column conductor 201 generates a magnetic field Hy and a current ly flowing in the row conductor 213 generates a magnetic field Hx. The combined effect of the magnetic fields (Hy, Hx) acting on the alterable orientation of magnetization causes the alterable orientation to flip if a combined magnitude of the magnetic fields (Hy, Hx) is of a sufficient magnitude.
One disadvantage of the prior magnetic tunnel junction device 200 is that shorts created during a manufacturing of the device can significantly reduce manufacturing yields. For example, if during the manufacturing of the prior magnetic tunnel junction device 200, some of the material for the column conductor 201 comes into contact with the row conductor 213 or comes into contact with a side 230c of the magnetic tunnel junction stack 230, then the magnetic tunnel junction device 200 is defective due to a short circuit.
In FIG. 2, the prior magnetic tunnel junction stack 230 can include a pinned layer 209 of a magnetic material (e.g. made from nickel iron NiF) and including a pinned orientation of magnetization (not shown), a tunnel barrier layer 207 (e.g made from aluminum oxide Al2O3 for a TMR device), and a data layer 205 of a magnetic material (e.g. made from nickel iron cobalt NiFeCo) and including an alterable orientation of magnetization (not shown). During manufacturing, a pattern formed by a mask layer 220 is formed on a dielectric layer 221. Ideally, as depicted by dashed lines I, the pattern formed by the mask 220 would be perfectly aligned with the magnetic tunnel junction stack 230. However, in reality, there are errors introduced by the machines and the fabrication processes used to manufacture the prior magnetic tunnel junction device 200. As a result, an actual misalignment depicted by dashed lines A can occur.
In FIG. 3, the dielectric layer 221 is etched through the mask layer 220 to form a via 233 in the dielectric layer 221. Due to the misalignment, the via 233 extends beyond a top portion of the magnetic tunnel junction stack 230 and exposes a side portion 233m of the magnetic tunnel junction stack 230.
In FIG. 4a, during a metal deposition step, an electrically conductive material 235 fills in the misaligned via 233 including those portions in the side portion 233m which creates a short 235s between the magnetic tunnel junction stack 230 and the row conductor 213. In FIG. 4b, the column conductor 201 is formed on the electrically conductive material 235 resulting in a short 235t between the row and column conductors (213, 201) and the magnetic tunnel junction stack 230.
Consequently, there is a need for a method of making a magnetic tunnel junction device that reduces the potential for electrical shorts due to misalignment of a via relative to a magnetic tunnel junction stack.